Electronic components such as power transistors are in many cases configured by joining electronic elements, such as semiconductor elements, directly to at least one electrode.
FIG. 7 is a view of an exemplary conventional power transistor, providing a partial perspective of a casing. The transistor 100 shown as an example has a semiconductor element 104 disposed within the casing 102 and directly joined to one electrode 106. The semiconductor element 104 is also connected to two other electrodes 108 and 110 via wires. Such a conventional power transistor typically uses solder at a joint for joining the semiconductor element 104 directly to the aforementioned one electrode.
Solder is also used at a joint for mounting the electronic component, such as a power transistor, onto another board. Most solder materials used for mounting the electronic component, such as a power transistor, onto another board have a melting point of from 200 to 230° C.
For soldering in such a case, joining is generally carried out by means of a solder immersion-type dip device. In this case, the solder material is required to be heated to 250 to 260° C., and therefore, in some cases, the temperature of the electrode in the electronic component reaches 250 to 260° C. Accordingly, in the case where the solder material at the joint for internally joining the electronic element in the electronic component to the electrode has a melting point of from 200 to 230° C., the solder material at the joint of the electronic element and the electrode might melt when soldering the electronic component to another board. Melting of the solder material at the joint of the electronic element and the electrode might result in occurrence of short-circuit and/or wire disconnection and/or a change in electrical characteristics, so that a final product becomes defective.
Therefore, it is necessary to use a solder material having a higher melting point as the solder material at the joint of the electronic element and the electrode. Proposed as such a solder material is a solder material having a melting point of 270° C. or higher and containing Bi (bismuth) and a small amount of Cu (copper) (see Patent Document 1).